The subject matter disclosed herein relates to insulation in electrical motors and generators, and more specifically to methods and systems related to stator insulation.
Electrical motors and generators may employ an architecture that has a rotor that is magnetically coupled to a stator. In some designs, the stator may have coils that conduct large currents and are responsible for the creation and maintenance of the magnetic fields driving the electrical machine. In order to prevent short-circuit between the coil and the stator core, as well as between the windings in the coil, the coils may be covered with insulating materials. During operation of the electrical machines, these insulating materials may be subjected to large electric fields.
The insulation in coils may have imperfections such as air pockets or air gaps. For example, when an insulating tape is wrapped around metal bars that form the coil, undesired air gaps may appear between different layers of the insulating tape, around the edges of the tape, and between the tape and the conductor. During operation of the electrical machines, the large electric potential differences may generate very large electric fields in these air gaps. If the electric field becomes larger than a breakdown electric field of the air gap, partial discharge (PD) events may occur. Ionization of gases and electrical discharges due to PD events often lead to damage in the insulation material, leading to degradation in the performance and eventual failure of the electrical machine. Current solutions to the presence of PD in the insulation material for electrical machines are generally related to choice of material that resists PD damage, such as mica-based insulation. In electrical machines with large size and highly complicated winding structure, insulation applied using a lapped-tape system may be more reliable and cost-effective in spite of the presence of air gaps and voids, and resulting PD activity.